Development and optimisation of sodium alginate and chitosan edible films with sea fennel by-product extract for active food packaging

Sea fennel by-product (woody stems and flowers), rich in phenolic compounds, possesses strong antioxidants and antimicrobial properties, making it a promising ingredient for sustainable food packaging. Utilizing plant-based by-products in biopolymer films can enhance their functional properties while promoting waste valorisation and environmental sustainability. This study aimed to develop and optimise sodium alginate-chitosan edible films incorporated with sea fennel by-product extract (SFBPE) for improved antioxidant activity, barrier properties, and food preservation applications. The films were optimised using central composite design response surface methodology (CCD-RSM), characterised, and applied as an edible coating for fresh strawberries. The optimal formulation contained 6.0 mL/100 mL SFBPE, 1.5 g/100 mL sodium alginate, 1.1 g/100 mL chitosan, and 1.5 mL/100 mL glycerol, yielding a film with a thickness of 0.085 mm, tensile strength of 5.77 MPa, and water contact angle of 77.9°. Incorporating SFBPE enhanced total phenolic content, antioxidant activity, hydrophobicity, and opacity of the optimised film compared to the control (without SFBPE), with only a minor reduction in mechanical properties. The lightness of the films decreased by 21.92 % with SFBPE addition. Spectroscopic analysis confirmed strong interactions between the polymeric matrix and the SFBPE. The SFBPE-containing coating effectively preserved the freshness of strawberries for up to 13 days in cold storage, demonstrating its potential as a sustainable food packaging solution.